JP2010049001A - Image capturing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an image capturing apparatus capable of photographing an image free from defocus when observed, regardless of insertion and removal of an IRCF to/from an optical path. <P>SOLUTION: The image capturing apparatus includes: an imaging optical system including a focus lens; an imaging means for converting an image, formed by the imaging optical system, into an electrical video signal; a wavelength band selecting means insertable into or retractable from the optical path of the imaging optical system and used for selecting a specific wavelength band; an insertion and removal means for inserting the wavelength band selecting means into the optical path or retracting it therefrom; and a focusing means for driving the focus lens of the imaging optical system and focusing it. When the insertion and removal means inserts the wavelength band selecting means into the optical path or retracting it therefrom, the focusing means focuses the imaging optical system. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an imaging apparatus suitable for mounting an infrared light removal filter in an optical path of an imaging optical system so as to be detachable and shooting with only visible light and shooting with light including infrared light. Is.

  2. Description of the Related Art Conventionally, an imaging apparatus for obtaining an object image has a photographing lens that forms incident light and an imaging element that converts an optical image formed by the photographing lens into an electrical signal. Furthermore, it has a signal processing means for obtaining a predetermined image signal by performing various kinds of signal processing on the electrical signal obtained from the image sensor.

  Usually, in an image pickup apparatus using a single plate type sensor using only one image pickup element such as a CCD sensor or a CMOS sensor, a different color filter is provided for each pixel.

  In order to obtain color signals of red (R), green (G), and blue (B) light, R, G, and B primary color filters that transmit light bands corresponding to R, G, and B color light are used. In some cases, complementary color filters such as magenta (Mg), cyan (Cy), and yellow (Ye) may be used.

  Each of the above color filters is designed to have a spectral transmission characteristic so as to transmit a target color using a dye or a pigment. Each of these color filters has a constant transmittance even in the near infrared region.

  In addition, the photoelectric conversion unit of the image sensor is mainly composed of a semiconductor such as silicon (Si). For this reason, the spectral sensitivity characteristic of the photoelectric conversion unit has sensitivity up to near infrared light having a long wavelength. Therefore, a signal obtained from an image sensor provided with a color filter includes a signal in the near infrared region.

  On the other hand, the color vision characteristic, which is a sensitivity characteristic for human colors, and the relative visibility characteristic, which is a sensitivity characteristic for brightness, range from a wavelength of 380 nm to a wavelength of 780 nm. In this sensitivity characteristic, there is almost no sensitivity in a wavelength region longer than the wavelength of 700 nm.

  Therefore, in many image pickup apparatuses, in order to match color reproducibility with human color vision characteristics, an infrared light removal filter for correcting visibility that does not allow light in the near infrared region to pass in front of the image sensor (on the light incident side) ( Hereinafter referred to as IRCF).

  On the other hand, many image pickup apparatuses are provided with an automatic focus adjustment mechanism. As one of the automatic focus adjustment mechanisms, the focus lens of the photographing lens is driven at a predetermined driving step, and high frequency components of an image signal obtained via the photographing lens and the image sensor are extracted at predetermined time intervals. A so-called TVAF system is known in which a focus lens is driven to a position showing the maximum value of a high-frequency component, and a photographing lens is focused.

  For example, in the case where sensitivity is more important than color reproducibility as an imaging device, light in the near infrared region is used. For this reason, the IRCF is retracted from the optical path, and near-infrared light is received by the image sensor to image the subject.

  When the IRCF is inserted into and removed from the optical path, the optical path length changes by an amount corresponding to the wavelength of incoming light and the thickness of the IRCF.

  Therefore, the focus position of the photographic lens differs depending on the insertion / removal of the IRCF from the optical path, and the optimum focus lens drive range differs in an imaging apparatus using the TVAF method that detects a high-frequency component of an image signal.

In order to solve such a problem, an imaging apparatus is known in which the position of the focus lens and the drive range of the focus lens are changed depending on whether the IRCF is inserted into the optical path or not. (Patent Document 1).
JP 2002-221656 A

  An imaging apparatus having a mechanism that varies the drive range of the focus lens depending on whether or not it is in the IRCF optical path facilitates highly accurate focus detection by the TVAF method.

  In Patent Document 1, the insertion / extraction status of the IRCF from the optical path is determined simultaneously with the release switch being pressed. In an imaging device such as a video camera that continuously shoots, the IRCF may be inserted and removed from the optical path during shooting. In this case, an out-of-focus image is shot after the IRCF is inserted and removed until the focus lens moves and the focus lens drive range is set. This is not very preferable in terms of photography.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image pickup apparatus that can take an image that is not out of focus in observation even when an IRCF is inserted into or removed from an optical path.

An imaging apparatus according to the present invention includes an imaging optical system including a focus lens, an imaging unit that converts an image formed by the imaging optical system into an electrical video signal,
A wavelength band selecting means that is detachably provided in the optical path of the imaging optical system, and that selects a specific wavelength band;
Inserting / removing means for inserting / removing the wavelength band selecting means from the optical path;
Focus adjustment means for driving the focus lens of the imaging optical system and performing focus adjustment;
In accordance with the insertion / removal of the wavelength band selection unit from the optical path by the insertion / removal unit, the focus adjustment unit adjusts the focus of the imaging optical system.

  According to the present invention, it is possible to obtain an imaging apparatus that can capture an image that is not out of focus on observation even when the IRCF is inserted into and removed from the optical path.

  Embodiments of an imaging apparatus according to the present invention will be described below in detail with reference to the accompanying drawings.

  The imaging apparatus of the present invention converts an image formed by an imaging optical system including a focus lens into an electrical video signal by an imaging means such as a CCD.

  A wavelength band selecting means for selecting a specific wavelength band (for example, infrared light) is inserted into and removed from the optical path by the inserting / removing means in the optical path of the imaging optical system.

  Focus adjustment means for adjusting the focus by driving the focus lens of the imaging optical system is provided.

  As the wavelength band selection unit is inserted into and removed from the optical path, the focus adjustment unit moves the focus lens to a preset position, or changes the focus lens drive range, etc., to adjust the focus of the imaging optical system. ing.

  FIG. 1 is a main part configuration diagram of Embodiment 1 of the present invention.

  In FIG. 1, reference numeral 1 denotes an imaging lens (imaging optical system). Reference numeral 2 denotes an infrared light removal filter (IRCF). Reference numeral 3 denotes a CCD (imaging means) (imaging device). The light from the subject incident from the imaging lens 1 forms an image on the light receiving surface of the CCD 3.

  Reference numeral 4 denotes an AD conversion unit which AD-converts an analog signal from the CCD 3 and converts it into a digital signal. A video signal processing unit 5 performs color conversion, AE processing, and WB processing on the digitized signal from the AD conversion unit 4.

  Further, various image processing such as γ processing for performing tone conversion of the signal-processed video is performed. Also, AF information H used for AF (automatic focusing) is calculated from the contrast value of the subject. Also, luminance information Y used for IRCF insertion / extraction determination is calculated. A video signal output unit 6 outputs video.

  Reference numeral 7 denotes an IRCF insertion / removal determination unit that determines whether or not IRCF2 is inserted / removed in / from the optical path. For example, IRCF insertion / removal determination is performed based on the luminance information Y calculated by the video signal processing unit 5.

  Normally, when the luminance information Y is sufficiently large, the IRCF 2 is inserted into the optical path, the image is taken without using light in the near infrared region, and a color image is output.

  When the luminance information Y becomes small, taking advantage of the fact that the CCD 3 also has sensitivity in the near infrared region, the IRCF 2 is extracted from the optical path length, and photographing is performed.

  By removing IRCF2 from the optical path, near-infrared light is also received and sensitivity is improved. An IRCF control unit 9 inserts and removes IRCF 2 according to an instruction from the IRCF insertion / extraction determination unit 7. Reference numeral 8 denotes a focus processing unit, which performs focus adjustment of the photographing lens 1 based on AF information H that is an AF evaluation value calculated by the video signal processing unit 5 during autofocus (automatic focus detection) (hereinafter referred to as AF). .

  Further, during manual focus (hereinafter referred to as MF), the photographing lens 1 is driven and controlled so that the subject distance information D is in focus. The lens control unit 10 moves the focusing lens (focus lens) of the photographing lens 1 to the lens position information designated by the focus processing unit 8.

  FIG. 2 is a schematic diagram of the configuration of the IRCF 2 in FIG. Reference numeral 20 denotes an IRCF. During normal photographing, light passing through the photographing lens 1 passes through the IRCF 20 and is received by the CCD 3. Reference numeral 21 denotes a transmission region of visible light and infrared light, which is made of a dummy glass or a simple empty frame and transmits a wavelength component (infrared component) cut by the IRCF 20.

  When the subject brightness is low, the IRCF 20 is positioned outside the optical path and the transmission region 21 is positioned in the optical path in order to increase sensitivity using near infrared light. Thereby, the light beam is condensed on the CCD 3 through the transmission region 21.

  In the transmission region 21, it is preferable to put a dummy glass having an optical path length (thickness) similar to that of the IRCF 20 so that the optical path length is not changed by the thickness of the IRCF 20. An IRCF frame (holding means) 22 holds the IRCF 20.

  FIG. 3 is an explanatory diagram showing the spectral characteristics of the CCD 3 and the transmission spectral characteristics of the IRCF section 20. In the case of a primary color CCD, R, G, and B have spectral characteristics that take color filters into account. IRCF has a spectral characteristic that removes light having a wavelength longer than that of the near infrared.

  By removing the IRCF unit 20 from the optical path, light is received even for light having a wavelength longer than the wavelength of about 650 [nm] that has been removed by the IRCF unit 20, so that sensitivity can be increased.

  On the contrary, the sensitivity of the R component is significantly increased due to the influence of near-infrared light, so that the color balance is lost, and the IRCF section 20 is normally inserted into the optical path for photographing.

  Next, the focus adjustment of the taking lens 1 when the IRCF 2 is extracted from the optical path in the present invention will be described.

  In cameras that are used day and night, such as surveillance cameras, when the brightness is sufficient during the day, IRCF 2 is inserted into the optical path to output a color image. When lightness becomes insufficient at night, sensitivity is more important than color reproducibility due to the effect of noise due to gain.

  In that case, in order to use light in the near infrared region in addition to visible light, the IRCF 2 is retracted out of the optical path and the image sensor 3 receives near infrared light.

  At this time, if the IRCF 2 is simply retracted from the optical path, the focus position changes by the optical path length of the IRCF 2. For this reason, a dummy glass may be inserted into the transmission region 21 so that the optical path length is not changed by inserting / removing the IRCF 2.

  When there is no dummy glass, the optical path length changes. For this reason, it is necessary to change the position or driving range of the focus lens set in advance for focusing or to follow the focus lens by the change in the optical path length.

  The change value of the optical path length at this time is stored in the focus processing unit 8 in advance. In addition, the light source determination unit 11 is provided in the configuration of FIG. 1 and the configuration of the light source determination unit 11 is configured as shown in FIG. In addition to the minute, the focus amount based on the wavelength (the spectral characteristic of the illumination light) may be corrected.

  When shooting a subject with manual focus by a surveillance camera, it is necessary to always maintain the focus of a desired subject distance. If the focus tracking is performed after the IRCF 2 has taken a predetermined time from the optical path, a period during which the focus cannot be maintained at the best position occurs between the insertion and removal of the IRCF 2 and the focus tracking.

  Therefore, it is preferable to follow the focus in conjunction with the insertion / extraction of IRCF2. Further, there is a possibility that the focus follow-up operation for maintaining the best focus position by inserting / removing the IRCF 2 may be noticed by the user (photographer).

  In this embodiment, for example, when a scene as shown in FIG. 4 is shot, there is a moment when a part of the IRCF frame 22 passes on the imaging screen of the imaging means 3 as shown in FIG. . Therefore, the focus lens is caused to follow in conjunction with IRCF2 and within a time during which the IRCF frame 22 passes through the imaging screen.

  In this embodiment, at least a part of the IRCF frame 22 (holding means) that holds the IRCF 20 performs the focus adjustment set in advance by the focus adjustment means while passing through the imaging screen of the imaging means.

  In particular, in this embodiment, the IRCF frame (holding means) 22 is longer than the time required for passing the imaging screen 3 (first time) and shorter than the time required for the IRCF 20 to be inserted into and removed from the optical path (second time). To adjust the focus.

  As a result, the focus shift due to the insertion / extraction of the IRCF 2 is eliminated, and the change from the image that is out of focus to the image that is in focus is delayed, so that the focus can be followed without being noticed by the user (photographer).

  Next, focusing by IRCF2 insertion / extraction during manual focusing will be described using the flowchart of FIG. When the luminance information Y of the subject decreases and the luminance information Y becomes smaller than the threshold Yth, the IRCF insertion / removal determination unit 7 sends an IRCF2 extraction instruction to the IRCF control unit 9, and the IRCF2 is removed from the optical path. Extracted. At this time, the information from which IRCF2 is removed is also sent from the IRCF insertion / removal determination unit 7 to the focus processing unit 8 (S601).

  The focus processing unit 8 determines whether the IRCF frame 22 is passing the imaging screen based on the IRCF2 position information from the IRCF control unit 9 (S602).

  At this time, even if the IRCF control unit 9 does not make a determination based on the IRCF2 position information, the time from the IRCF2 insertion / removal instruction from the IRCF insertion / removal determination unit 7 is counted to determine whether the IRCF frame 22 is passing through the imaging screen. You may judge whether.

  If the IRCF frame 22 is passing the shooting screen in S602, the focus lens that constitutes the shooting lens 1 is followed, and focus correction corresponding to the insertion / removal of the IRCF 2 is performed. In addition, when the driving range of the focus lens is varied depending on the insertion / removal state of the IRCF frame 22, the driving range of the focus lens may be changed in conjunction with the insertion / removal of the IRCF2.

  As described above, the focus shift caused by driving the IRCF2 can be corrected by following the focus lens as the IRCF2 is driven.

  Further, by causing the focus lens to follow while the IRCF frame 22 passes through the photographing screen, the focus movement operation by the focus lens can be performed without being noticed by the user, and an uncomfortable image can be observed.

  Embodiment 2 of the present invention will be described.

  The configuration of the second embodiment is the same as that of the first embodiment shown in FIG.

  Next, focus adjustment of the taking lens 1 when the IRCF 2 is extracted from the optical path in the second embodiment will be described.

  In cameras that are used day and night, such as surveillance cameras, when the brightness is sufficient during the day, IRCF 2 is inserted into the optical path to output a color image. When lightness becomes insufficient at night, sensitivity is more important than color reproducibility due to the effect of noise due to gain.

  In that case, in order to use light in the near infrared region in addition to visible light, the IRCF 2 is withdrawn out of the optical path and the image sensor 3 receives near infrared light.

  At this time, since the photographing optical path length changes by the optical path length of IRCF2, a dummy glass is inserted into the transmission region 21 so that the optical path length is not changed by insertion / extraction of IRCF2. When there is no dummy glass, the optical path length changes. Therefore, it is necessary to change the driving range of the focus lens in order to focus, and to follow the focus lens by the change in the optical path length.

  When a subject is photographed with manual focus by an operation from the outside with a surveillance camera, the focus of a desired subject distance must always be maintained. If tracking of the focus lens is performed after IRCF2 is removed and a predetermined time is required, a period during which the focus cannot be maintained occurs between insertion and removal of IRCF2 and focus tracking.

  Therefore, the focus lens follows the preset position in conjunction with the insertion / extraction of the IRCF 2 from the optical path.

  Furthermore, there is a possibility that the focus lens tracking for maintaining the focus by inserting the IRCF 2 may be noticed by the user. Therefore, the image is gradually changed so as to be improved by sufficiently slowing the focus speed when the focus lens follows. According to this, it is possible to eliminate the instantaneous movement of the focus follow-up and perform the focus adjustment without being noticed by the user.

  Here, the focus speed at the time of following the focus will be described. The time required until the IRCF frame 22 starts to appear on the screen and the IRCF frame 22 disappears from the screen is approximately 10 V to 60 V, and it takes time for a person to recognize the passage of the IRCF 2. Here, 1V is 1/60 second.

  The amount of movement of the focus lens required to follow the focus is sufficiently smaller than the amount of movement of IRCF2. By following at such a speed as to follow the focus over the time required for the movement of the IRCF frame 22, it is possible to prevent the user from noticing a sudden change in the image due to the movement of the focus following. .

  However, after that, it takes more time until the IRCF 20 and the transmission region 21 enter. If the IRCF 20 and the transmission region 21 are driven for a long time until they enter, the focus may not be able to follow even though the insertion and removal of the IRCF 20 is completed.

  Therefore, the focus follow-up is longer than the time required for the movement of the IRCF frame (holding means) 22 (first time) (longer) and shorter than the time required for completion of insertion / removal of the IRCF 20 (second time) (shorter). It is desirable to do.

  Further, the focus speed used for focus adjustment in manual focus (manual focus adjustment means) is moved at a sufficiently slow speed so that the image is stopped on the focus surface.

  For this reason, the focus lens focus speed is set slower than the focus speed used for focus adjustment in manual focus in focus follow-up accompanying insertion / removal of the IRCF in the optical path.

  That is, the speed of the focus lens of the imaging optical system when the focus adjustment is performed with the insertion / removal of the IRCF from the optical path is made slower than the speed of driving the focus lens of the imaging optical system by the manual focus adjustment means.

  As described above, by setting the speed at the time of following the focus sufficiently low, the focus movement operation by moving the focus lens can be performed without being noticed by the user, and an uncomfortable image can be obtained.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to these embodiments, and various modifications and changes can be made within the scope of the gist.

  For example, a color filter, an ultraviolet light removal filter, or the like may be used instead of the infrared light removal filter (IRCF).

Configuration diagram of Embodiment 1 of the present invention Configuration of IRCF in FIG. Explanatory diagram of the spectral characteristics of the CCD and the transmission characteristics of the IRCF in FIG. Explanatory drawing of an example of the imaging | photography scene on the image pick-up element surface at the time of IRCF insertion Explanatory drawing of an example of the imaging | photography scene on the image pick-up element surface during IRCF frame passage FIG. 1 is a control flow diagram of Embodiment 1 of the present invention. The block diagram of the other form of the Example of this invention

Explanation of symbols

1 Imaging optical system 2 Infrared light removal filter (IRCF)
3 Imaging means 4 AD conversion section 5 Video signal processing section 6 Video signal output section 7 IRCF insertion / removal determination section 8 Focus processing section 9 IRCF control section 10 Lens control section 11 Light source determination section 22 Holding means 20 IRCF
21 Dummy glass

Claims (5)

An imaging optical system including a focus lens; and an imaging means for converting an image formed by the imaging optical system into an electrical video signal;
A wavelength band selecting means that is detachably provided in the optical path of the imaging optical system, and that selects a specific wavelength band;
Inserting / removing means for inserting / removing the wavelength band selecting means from the optical path;
Focus adjustment means for driving the focus lens of the imaging optical system and performing focus adjustment;
An image pickup apparatus, wherein the focus adjustment unit performs focus adjustment of the image pickup optical system when the wavelength band selection unit is inserted into and removed from the optical path by the insertion / removal unit.   The imaging apparatus according to claim 1, wherein the driving range of the focus lens is changed in accordance with insertion / removal of the wavelength band selection unit from the optical path. Holding means for holding the wavelength band selecting means;
The imaging apparatus according to claim 1, wherein at least a part of the holding unit performs a focus adjustment preset by the focus adjustment unit while passing through an imaging screen of the imaging unit. Holding means for holding the wavelength band selecting means;
Longer than the first time required for the holding means to pass through the imaging screen of the imaging means,
The focus adjustment of the imaging optical system is performed by the focus adjustment unit in a time shorter than a second time required for insertion / removal of the wavelength band selection unit from the optical path. Imaging device. Manual focus adjustment means for adjusting the focus of the imaging optical system by an external operation;
Compared to the speed at which the focus lens of the imaging optical system is driven by the manual focus adjustment unit, the focus lens of the imaging optical system when performing the focus adjustment in accordance with the insertion / removal of the wavelength band selection unit from the optical path. The imaging apparatus according to claim 1, wherein the speed is low.